1. Field of the Invention
The present invention relates to position measurement of a portable electronic device. More particularly, the present invention relates to a method and apparatus for position measurement of a portable electronic device based on an Assisted-Global Positioning System (A-GPS) scheme.
2. Description of the Related Art
A position measuring technology may use Global Positioning System (GPS) satellites in various fields. In particular, the position measurement technology using GPS satellites may be used in position measurement of mobile terminals, vehicle/ship navigation devices, and for any position measurement of other similar and/or suitable electronic devices having a position measuring capability.
In the related-art, American GPS-based position measuring methods have been provided. However, recently, a Russian GLObal NAvigation Satellite System (GLONASS), a European Union (EU) Galileo system, and a Chinese Compass system are or will be provided. Environments capable of more accurate position determination are created through a Global Navigation Satellite System (GNSS). In particular, as a number of available orbiting satellites, from which information is collected, increases, the GNSS can reduce errors and determine more accurate positions.
However, while the number of available satellites increases, a frequency of fault occurrence of satellites may also increase. The GPS, which was provided in the early 1970s by the United States (US) Department of Defense (DoD) to track positions of objects, has achieved accuracy and stability through long-term use. However, the GLONASS, which has recently been provided, has a relatively high frequency of fault occurrence and has lower stability and reliability than the GPS. Also, like the GLONASS, the Galileo system and the Compass system, which have been newly provided, may have low stability and reliability in their early stages. However, since not using available resources due to stability and a reliability may limit available position measurements, and thus may be a dilemma, there is a need for a method that can provide the maximum reliability in the existing use environment.
A related-art technology uses a Fault Detection (FD) technique or a Fault Detection and Exclusion (FDE) technique of a Receiver Autonomous Integrity Monitoring (RAIM) algorithm in order to exclude a faulty satellite signal from position measurement. In a GPS-based position determining method, a distance may be calculated and determined according to a time difference of a satellite signal between transmitting and/or receiving ends. Herein, when information of a specific satellite, that is used as a sample, is unhealthy, the information of the specific satellite should be excluded from a position measurement calculation. This process is performed by the FDE of the RAIM. The RAIM is often used for integrity monitoring in GPS navigation. The RAIM may improve the reliability of positions detected by devices using the GPS, by determining low-performance satellites and excluding at least one of such satellites from a position calculation at a time. The GPS typically needs at least four satellites in order to detect the position of an aircraft. Since an additional satellite should be used in order to use the RAIM, five satellites are typically needed in order to perform the FD.
That is, in order to provide for a case where currently-transmitted navigation information has an error due to a failure of a GPS satellite or a terrestrial observatory, a receiver may determine integrity of GPS satellite information, and accordingly, a user may exclude a satellite that provides wrong information or has a poor signal state or quality.
However, in a relate-art FDE method, an excluded satellite may not be recovered, i.e., used again, unless a device or the FDE method is artificially reset. In an actual live environment, the GPS and the GLONASS may be used in a mixed manner, and all available satellite information of the GPS and the GLONASS may be provided in an initial execution stage. However, in the case of the GLONASS that has relatively frequent faults and malfunctions, unhealthy satellite information may be increasingly excluded by the FDE method over time. As a result, in some cases, all GLONASS satellites determined to be available are also excluded by the FDE method, and only GPS satellites are used. Accordingly, the GLONASS is excluded and only the GPS is used even when the GPS and the GLONASS may be used together.
However, since a satellite may be excluded as an unhealthy state continues to be detected in a terrestrial observatory, even when the satellite has been excluded as an unhealthy state in a portable electronic device, the satellite may actually have been recovered and may currently be in a healthy state.
Therefore, a need exists for a system and method for a method and apparatus for position measurement of a portable electronic device based on an Assisted Global Positioning System (A-GPS) scheme.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.